1. Field of the Invention
This invention relates to a hot-melt ink used in ink-jet recording apparatus. More particularly, it relates to a hot-melt ink used in ink-jet recording apparatus in which ink is heated to melt in a state of higher temperature than room temperature to make a record.
2. Description of the Related Art
As ink-jet recording systems, various systems are proposed, e.g., what is called an electric field control system, in which the direction of fly of continuously ejected ink is deflected by an electrostatic attraction force; what is called a drop on-demand system (or pressure pulse system), in which the pressure applied to ink chambers is controlled by utilizing the vibration of a piezoelectric device, to eject ink; and what is called a thermal ink-jet system, in which a pressure produced by bubbles formed and grown by locally heating ink in capillaries is utilized to eject ink. These systems can provide very highly precise printed images.
As inks used in these ink-jet recording systems, water-based inks employing water as a main solvent or oil-based inks employing an organic solvent as a main solvent are commonly used. Printed images obtained using the water-based inks have a poor water resistance in general. On the other hand, the use of oil-based inks can provide printed images having a good water resistance.
However, these water-based inks and oil-based inks are liquid at room temperature, and hence feathering tends to occur because ink rapidly permeates into a recording paper when images are printed on the recording paper, and that a sufficient print density has been achievable with difficulty. Also, because these inks are liquid, they tend to cause formation of deposits such as aggregates of dyes from inks during their storage, and such deposits have caused a great lowering of the reliability of ink-jet recording systems because of, e.g., clogging of nozzles.
Accordingly, in order to overcome such disadvantages of the conventional inks of a solution type, there is proposed a hot-melt ink-jet recording system making use of inks which are solid at room temperature and melt upon heating, and there are proposed various hot-melt inks used in the ink-jet recording system of this type.
For example, U.S. Pat. No. 3,653,932 discloses an ink containing a dialkyl sebacate. U.S. Pat. No. 4,390,369 and Japanese Patent Application Laid-open No. 58-108271 disclose an ink containing a natural wax. Japanese Patent Application Laid-open No. 59-22973 discloses an ink containing a stearic acid. Japanese Patent Application Laid-open No. 61-83268 discloses an ink containing an acid or alcohol having 20 to 24 carbon atoms and also containing a ketone having a relatively higher melting point than these. Japanese Patent Application Laid-open No. 62-48774 discloses an ink containing a thermosetting resin having a high hydroxyl value, a solid organic solvent having a melting point lower than 150.degree. C. and a small quantity of a dye substance. Japanese Patent Application Laid-open No. 62-112627 discloses an ink comprised of a colorant, a first solvent which is solid at room temperature and capable of liquefying upon heating to a temperature higher than the room temperature and a second solvent capable of dissolving the first solvent, being liquid at room temperature and being highly volatile. Japanese Patent Application Laid-open No. 62-295973 discloses an ink containing a synthetic wax having a polar group and a dye soluble in the wax.
However, none of these conventional hot-melt inks well satisfy transparency of ink, color stability during storage, and good print quality such as recording density and hue. In particular, the poor dispersibility or solubility of dyes in main components of ink has a great influence on these properties or performances. Also, with the progress of office automation in recent years, there is an increasing demand for color presentation mediums such as color OHPs (overhead projectors). In order to meet such a demand, hot-melt inks are required to have a transparency for color reproduction of projected images, an adhesion to OHP films, and a heat resistance when used. However, hot-melt inks that can satisfy all of these requirements have not been available.